Diameter, circumference, area

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define pi 3.14159

int main()
{

    float r,d,c,a;
    printf("Enter radius=\n");
    scanf("%f",&r);
    d=2*r;
    printf("The diameter= %f\n",d);
    a=pi*pow(r,2);
    printf("The area= %f\n",a);
    c=2*pi*r;
    printf("The circumference= %f\n",c);
    return 0;
}